According to the yearly survey conducted by the state’s Pollution Control Board, the average Respirable Suspended Particulate Matter (RSPM) levels have plummeted by 45 per cent across the city. The average RSPM levels for the five centres which were monitored in Chennai city were 105.6 microgram per cubic metre — a significant decrease compared to last year’s average of 192.6 micro gram per cubic metre for Deepavali day last year.

“This year, particulate matter level has come significantly down compared to last year due to the rains,” said K Karthikeyan, member secretary, TNPCB. Among the individual centres, Nungambakkam saw the highest levels of RSPM at 131 microgram per cubic metre — down from 180 last year, while T Nagar came next, at 126, down from 180 last year.

“When there is rain, emissions get washed out of the air, especially the larger particulates. Sulphur di-oxide and nitrogen dioxide, the major air pollutants also get precipitated,” said Karthikeyan.

Chennai has also fared a lot better compared to many other cities of India this Deepavali. As of 4 pm on November 11, the average Air Quality Index calculated by the Central Pollution Control Board was at 159, significantly lower than Delhi and Faridabad, with 343 and 378 respectively. Other cities like Kanpur, Varanasi, Patna, Pune and Agra also saw significantly worse levels. Mumbai saw AQI at 177 and Bengaluru at 56.

“Chennai is usually better than the interiors because of its tropical climate and wind movements. We see a lot of vertical mixing in the atmosphere, which also helps in clearing out the air,” said Karthikeyan. The city also saw noise pollution levels for most centres this Deepavali come down.

The average noise pollution levels for the five centres were at 80.2 leq dB(A) — down from 80.4 last year. However, while Triplicane, Nungambakkam and Sowcarpet saw levels falling, and T Nagar only saw levels rise by 1 dB(A), Besant Nagar saw noise pollution levels rise by a significant 10 dB(A).